Your experiences of aftermarket suspension on the Z4 MC

[exdos]

the effective spring rate of the stock rear spring of 800lbs????? sorry john but thats just completely wrong.,

Byron,

This is the response that I had to an enquiry to Eibach about its lowering springs for the Z4MC.
Hi John,

Yes, it looks like they have been given out there, perhaps as a one off. On this occasion I will give you the rates for our Z4 M Coupe kit to help you out - I haven’t heard back yet if we can get hold of the BMW rates, if we can I will let you know.

Front: Progressive spring, initial rate is 23N/mm and the end rate is 34N/mm
Rear: Progressive spring, initial rate is 70N/mm with the end rate of 140N/mm.

I hope this answers your question, if you need anything else feel free to ask.

You can do the maths from that. But as you can see, the final spring rate of those rears is more than FOUR TIMES greater than the fronts, whereas most aftermarket set ups are much closer matched, front to rear, than that.

Obviously, your Z4MR, being supercharged with considerably increased HP and torque is NOT the same animal as an otherwise OEM Z4MR/MC and requires a totally different suspension for your needs as a track-focussed car. I know that I would also have gone for KW Clubsport if I supercharged my Z4MC. At the end of the day, it's horses for courses

 

[Beedub]

how about this kit for a complete halfway point combined with the eibach setup??? cost effective and bound to be a really nice middle point!! actually think thats a great idea.

http://www.turnermotorsport.com/p-1584-z4m-bilstein-hd-shock-package-mz4-roadster-coupe-4-shocks.aspx

we'll have to agree to disagree on this one john for me an EFFECTIVE spring rate on a progressive spring means jack all..... lets talk about actual spring rates, actual damping and valving used and the FEEL that they equate to...... i spoke to TCKline racing, about their D/A track kit and told me a spring rate on the rear of 700lb would lead to a near unbearable ROAD vehicle, if you telling me the stock is an 800lb spring rate, then.... like i say ill agree to disagree. Like i say the word EFFECTIVE is misleading in this context.

you've nailed it..... horses for courses.

braking hard in my car with the stock setup was plain scary..... the car would stand on its noise and the back would start to move out...... when the car was stock however, i loved the stock suspension with alignment changes, not ideal but, pretty damn good imo...... see the video below stopping from 100mph.... as i finish the straight line dash and begin braking, the car need corrective steering under braking..... fucking scary on a track with no run off.

http://www.youtube.com/watch?v=so5q1NVOIC4

 

[Beedub]

i do however think the blistein HD kit with eibach springs, would make a really nice kit!! Its a great price, really is.... so who's going to try it??

 

[kerstien]

Thanks for the feedback guys. Exdos do you know which intron kit is similar to the schnitzer and v3 models. Just sent them an email. Online looters port world seems the cheapest for the v3 option.

Thanks

Kerstien

 

[exdos]

how about this kit for a complete halfway point combined with the eibach setup??? cost effective and bound to be a really nice middle point!! actually think thats a great idea.

That kit uses the OEM springs and even if used in conjunction with Eibach springs, from the spring rates given to me by Eibach (as quoted above) I think the complete mismatch of F:R spring rates of 1:4 is a problem. Most adjustable aftermarket kits for the Z4MC are in the order of a spring rate ratio of around 1:1.2 or so: that's some difference! If I were to consider an unadjustable suspension kit, I'd want to be assured by the manufacturer that the F:R spring rates were in the ballpark of 1:1.2 with a front spring rate of around 400lbs/inch

we'll have to agree to disagree on this one john for me an EFFECTIVE spring rate on a progressive spring means jack all..... lets talk about actual spring rates, actual damping and valving used and the FEEL that they equate to...... i spoke to TCKline racing, about their D/A track kit and told me a spring rate on the rear of 700lb would lead to a near unbearable ROAD vehicle, if you telling me the stock is an 800lb spring rate, then.... like i say ill agree to disagree. Like i say the word EFFECTIVE is misleading in this context.

DON''T SHOOT THE MESSENGER! That information comes directly from Eibach. The "actual" spring rate is a variable on a progressive spring which is related to the amount of compression, so it can't be quoted as a fixed rate, as is the case with a linear spring. In your KW Clubsport kit, your photographs show that the rear springs are progressive springs, so what is the ACTUAL spring rate of both front and rear springs of that kit?

Just for interest, the rear springs on the Z4MC are 19mm diameter for the 3 central coils, in comparison, the OEM rear ARB on a Z3MC is 18.5mm.

 

[exdos]

Exdos do you know which intron kit is similar to the schnitzer and v3 models. Just sent them an email.

Nitron is a relatively small company and from my telephone conversation with them, they do a suspension set-up for the Z4MC for around £1,800. You need to check that the rear dampers are NOT coilovers.

 

[original guvnor]

Reading this thread has proved dangerous (and very interesting) because I'm now thinking more and more about a suspension upgrade now next year and may postpone CSL wheels purchase as a result!

I am though very much a novice on the topic, however the useful contributions from Exdos and Beedub in particular have helped in this regard.

 

[Beedub]

how about this kit for a complete halfway point combined with the eibach setup??? cost effective and bound to be a really nice middle point!! actually think thats a great idea.

That kit uses the OEM springs and even if used in conjunction with Eibach springs, from the spring rates given to me by Eibach (as quoted above) I think the complete mismatch of F:R spring rates of 1:4 is a problem. Most adjustable aftermarket kits for the Z4MC are in the order of a spring rate ratio of around 1:1.2 or so: that's some difference! If I were to consider an unadjustable suspension kit, I'd want to be assured by the manufacturer that the F:R spring rates were in the ballpark of 1:1.2 with a front spring rate of around 400lbs/inch

we'll have to agree to disagree on this one john for me an EFFECTIVE spring rate on a progressive spring means jack all..... lets talk about actual spring rates, actual damping and valving used and the FEEL that they equate to...... i spoke to TCKline racing, about their D/A track kit and told me a spring rate on the rear of 700lb would lead to a near unbearable ROAD vehicle, if you telling me the stock is an 800lb spring rate, then.... like i say ill agree to disagree. Like i say the word EFFECTIVE is misleading in this context.

DON''T SHOOT THE MESSENGER! That information comes directly from Eibach. The "actual" spring rate is a variable on a progressive spring which is related to the amount of compression, so it can't be quoted as a fixed rate, as is the case with a linear spring. In your KW Clubsport kit, your photographs show that the rear springs are progressive springs, so what is the ACTUAL spring rate of both front and rear springs of that kit?

YES!!! we have a winner!! their is no fixed rate on a progressive spring.... finally we get their!!!!
the rear is a progressive, i havent written otherwise???? FROM ALL the companies ive dealt with the rear is progressive on the z4m for a very specific reason due to the design of the rear end, kw offer a conversion to a linear rear but completely steered me away unless the car is actually a race car, ive already told you i dont know the spring rates for the kit, nor am i bothered..... what im trying to tell you is its how it equate to feel....dont get your knickers in a twist i wont continually beat a dead horse but you not always right im afraid nor am i,...... progressive, linear, bla bla bla.... what it all boils down to is how it translate into the car imo..... what it boils down to is i wouldn't the clubsport for a DD car, that we both agree on, its a track focused kit.

lets be honest, the main reason you jumped into the ACS was because their was a used kit going cheap and theirs nothing wrong with that, id like to bet my bottom dollar you wouldnt have actually picked one up new, right???, but at least be honest about the pit falls as well... everything has a downside.... the clubsport has many downsides.

their are pitfalls to progressive springs, and vice versa, weve got stuck in this rutt of talking about springs rates..... we need to move away from that and concentrate on the main PURPOSE of the kit...... Valving is as import if not more important than spring rates.... nitron use a much softer spring (linear up front, progressive in the rear) with agressive valving to get to their track focused kit.

most kits have a specific Target.

V3- fast road
ACS- fast road
AST- option with linea - more track focused
Nitron - fast road unless you spec the race which is 3400 quid!
Clubsport - track biased
TCKline - track biased
Ground control - Track biased
psss9/10 fast road

theirs so many options...... BUT the question is how many offer a TRUELY better setup than stock??? i guess thats for the beholder to answer right?

 

[Beedub]

Exdos do you know which intron kit is similar to the schnitzer and v3 models. Just sent them an email.

Nitron is a relatively small company and from my telephone conversation with them, they do a suspension set-up for the Z4MC for around £1,800. You need to check that the rear dampers are NOT coilovers.

They DO NOT offer a rear barrel spring anymore, this has been dropped, they only offer a proper coilover for the rear, otherwise id probably have gone this route, this is what i was told By ben @ nitron, just 7-8 weeks ago.

 

[Beedub]

nice to battle it out with someone anyhow my choice for me came down to taking a bit of a risk really..... for me its payed off...... but their are alot of compromises that will offer the user a great setup....

i still think for a low priced setup the bilsten HD combined with the eibach springs is probably the best budget setup, many owners already have the springs so they could get the shocks for under 500 quid!! cost effective and quality components without going to the extreme, you dont need to spend £000s to do this right, of course imo. The stock setup is really that bad imo.... on a smooth track it can liberate some impressive lap times... its help back by horrific factory settings.

 

[BMWZ4MC]

braking hard in my car with the stock setup was plain scary..... the car would stand on its noise and the back would start to move out...... when the car was stock however, i loved the stock suspension with alignment changes, not ideal but, pretty damn good imo...... see the video below stopping from 100mph.... as i finish the straight line dash and begin braking, the car need corrective steering under braking..... f***ing scary on a track with no run off.

http://www.youtube.com/watch?v=so5q1NVOIC4

Beedub, is that video with entirely stock suspension, the car looks like it's riding lower than stock? Also, were the brakes standard, tyres good / well inflated, tarmac in good condition etc?
Only I've braked as hard as that from >100mph on track and I've never experienced the rear trying to overtake the front like that I agree, it would have scared the sh** out of me too!

 

[Beedub]

Reading this thread has proved dangerous (and very interesting) because I'm now thinking more and more about a suspension upgrade now next year and may postpone CSL wheels purchase as a result!

I am though very much a novice on the topic, however the useful contributions from Exdos and Beedub in particular have helped in this regard.

its been great to hash it out really and i think what it comes down to is How bad is the stock setup for you??? how would the stock dampers feel with the eibach kit??? id love to know??
why would YOU like to upgrade from stock??? where are you feeling its short comings? i guess what would be your aim for a new setup??

 

[Beedub]

braking hard in my car with the stock setup was plain scary..... the car would stand on its noise and the back would start to move out...... when the car was stock however, i loved the stock suspension with alignment changes, not ideal but, pretty damn good imo...... see the video below stopping from 100mph.... as i finish the straight line dash and begin braking, the car need corrective steering under braking..... f***ing scary on a track with no run off.

http://www.youtube.com/watch?v=so5q1NVOIC4

Beedub, is that video with entirely stock suspension, the car looks like it's riding lower than stock? Also, were the brakes standard, tyres good / well inflated, tarmac in good condition etc?
Only I've braked as hard as that from >100mph on track and I've never experienced the rear trying to overtake the front like that I agree, it would have scared the sh** out of me too!

bone stock, brakes were AP BBK, tyres ps2 inflated to 35psi HOT, tarmac at SDCC is very good, very smooth and grippy i dont know if the increased squat caused by all that power shifting to the front under hard braking causes the inbalance but basically the rears are loosing all grip with the tarmac, when im braking from those speeds and that happens i cant lie.... i crapped my pants!!! im pleased to this is has totally been eradicated!!
The car does however look really low on that clip, the only change id done to the stock setup is add camber and get simpson to get the settings as aggressive as possible..

 

[BMWZ4MC]

It shouldn't matter how the car got to 100mph (ie SC for you vs NA for me), braking will lead to the same transfer of weight if the rate of braking is the same. I can only thnk that you are decelerating at a greater rate than I can muster due to a combination of bigger brakes and stickier rubber.
I'll do some really hard brake tests in a couple of weeks when I'm next on the track, then I'll check my pants for Sepang stains and let you know

 

[Beedub]

It shouldn't matter how the car got to 100mph (ie SC for you vs NA for me), braking will lead to the same transfer of weight if the rate of braking is the same. I can only thnk that you are decelerating at a greater rate than I can muster due to a combination of bigger brakes and stickier rubber.
I'll do some really hard brake tests in a couple of weeks when I'm next on the track, then I'll check my pants for Sepang stains and let you know

You misread me my reasoning was due to a shed load of squat the transfer to the front end in a fast hard braking situation would unsettle the rear, the clip clearly shows the front compress hard into the floor. If I accelerate to 100 full power my car sits on its ass big time, or used to at least.

May well be sticky warm tyres combined with big brakes and track pads but, either way.... It was a scary feeling!!

Probably doesn't help with the added weight right on front of the car!!! Hence why I even more wanted a track focused setup.... Can't wait for more seat time !!!!

 

[bertman]

most kits have a specific Target.

V3- fast road
ACS- fast road
AST- option with linea - more track focused
Nitron - fast road unless you spec the race which is 3400 quid!
Clubsport - track biased
TCKline - track biased
Ground control - Track biased
psss9/10 fast road

This is an excellent summary and exactly what Newbs like me are looking for. All the above are coilover kits? or do some require a matched spring as well? if so which one

 

[Beedub]

most kits have a specific Target.

V3- fast road
ACS- fast road
AST- option with linea - more track focused
Nitron - fast road unless you spec the race which is 3400 quid!
Clubsport - track biased
TCKline - track biased
Ground control - Track biased
psss9/10 fast road

This is an excellent summary and exactly what Newbs like me are looking for. All the above are coilover kits? or do some require a matched spring as well? if so which one

all are a front coilover and rear barrell spring with sperate damper ( what you want on this car) you still get height adjustability front and rear with most kits listed. ACS is a fixed rear drop... not an issue at all imo.... most of those kits offer a progressive spring front bar the Ground control, TCK, Clubsport, these offer much less ride comfort.

 

[exdos]

YES!!! we have a winner!! their is no fixed rate on a progressive spring.... finally we get their!!!!
the rear is a progressive, i havent written otherwise???? FROM ALL the companies ive dealt with the rear is progressive on the z4m for a very specific reason due to the design of the rear end, kw offer a conversion to a linear rear but completely steered me away unless the car is actually a race car, ive already told you i dont know the spring rates for the kit, nor am i bothered..... what im trying to tell you is its how it equate to feel....dont get your knickers in a twist i wont continually beat a dead horse but you not always right im afraid nor am i,...... progressive, linear, bla bla bla.... what it all boils down to is how it translate into the car imo..... what it boils down to is i wouldn't the clubsport for a DD car, that we both agree on, its a track focused kit.

I don't see what you're getting so excited about. Eibach have been able to describe a progressive spring having an "initial" and "final" rate (with a range between those two poles) and linear springs have a fixed spring rate. Where's the problem? Obviously, we both disagree on the ride and handling of the OEM suspension, I think it's bad and you don't, therefore our subjective opinions vary, but somehow, we've both decided to ditch the OEM suspension for aftermarket stuff.

lets be honest, the main reason you jumped into the ACS was because their was a used kit going cheap and theirs nothing wrong with that, id like to bet my bottom dollar you wouldnt have actually picked one up new, right???, but at least be honest about the pit falls as well... everything has a downside.... the clubsport has many downsides.

I get the feeling that you feel that I am knocking your choice of Clubsports. I honestly think that Clubsports were the right choice for you, and they were certainly on my shortlist. If you'd fitted them sooner, then I would've been over to your place like a shot so that I could've had first hand experience of them before making my purchase. I make absolutely no secret of the fact that I opted for the ACS kit because of the price I got them for, but they were definitely on my shortlist as an alternative to KWV3, but I would probably have not bought the ACS kit because of their high price. I therefore feel I've got a real bargain with them.

My ideal adjustable suspension for the Z4MC doesn't actually exist as a commercially available kit, so any set-up I bought would always have to be a compromise. For me, so far, the downsides of the ACS is the fact that the rebound/bump adjusters on the dampers are combined, whereas on the KWV3 they are separate but stupid fiddly things that I didn't want. However, a single adjuster does make adjustment much simpler and quicker. Likewise, I would have preferred a linear front coilover, as on the KWV3 on my Z3MC, but from what I've read, the Clubsports are a track-focussed set-up and I didn't want to ditch the OEM suspension only to find that the Clubsports are too firm a ride for me for road use.

BUT the question is how many offer a TRUELY better setup than stock??? i guess thats for the beholder to answer right?

Because I've been unable to try any aftermarket suspension on a Z4MC before making my choice, I've had to rely solely on my experiences with my Z3MC, and what I know and have learned about vehicle dynamics/suspension over the years, and I'm afraid that for me, spring rates figure heavily in this. I did my "due dligence" on the ACS kit before buying and consequently, so far, they've performed exactly as I anticipated. For me, the ACS Racing suspension is a huge improvement over stock because it has been able to transform the quality of the ride (softer rear springs than OEM) and also correct the lifting and pitching of the front end (stiffer front springs than OEM). As I've said before, I couldn't live with an OEM Z4MC, but now my car has been transformed in the way that I wanted and I shall keep it and anjoy it for a long time! Yes, I now have a "winner" 8)

 

[original guvnor]

Reading this thread has proved dangerous (and very interesting) because I'm now thinking more and more about a suspension upgrade now next year and may postpone CSL wheels purchase as a result!

I am though very much a novice on the topic, however the useful contributions from Exdos and Beedub in particular have helped in this regard.

its been great to hash it out really and i think what it comes down to is How bad is the stock setup for you??? how would the stock dampers feel with the eibach kit??? id love to know??
why would YOU like to upgrade from stock??? where are you feeling its short comings? i guess what would be your aim for a new setup??

Principally to eliminate rock hard rear suspension, provide better (ie more comfortable) ride, stop traction control light coming on all the time on twisty b-roads. Not really noticed front-end lift or diving under braking that are troubling others but i'd be the first to admit i might not be as skilled a driver as some of you. A road set-up rather than track because I don't envisage tracking my car really.

 

[Beedub]

arhh john.... you get me all wrong, i KNOW your not knocking my choice for the track biased stuff i went with, if you did?? honestly? it wouldnt bother me, but i know your not.....
im not excited at all, i chuckled because i finally got you to say what i wanted you to say Their is no problem although your tone has changed somewhat which has amused me slightly more than it should..... your a great guy, great asset to the club but ive seen numerous occasions where people challenging you makes you come across defensive.

anyway back on subject and no more banter... we've bashed out our difference of opinion now and its done so we'll leave it their at this point and look forward to other chiming in with their feelings on how they would like to improve things......

some items, we agree on, some we dont....
The clubsport setup is most definitely NOT for most, its extreme.
i look forward to more time with them and see where we go.......

im glad you've found your winning formula!! im on the same road..... mines just a lilttle bumpier


i guess the question for ALL the readers??? how bad is stock for you??? what do you want from it and is it achievable at a decent price....

this is how a discussion should be....... ive enjoyed it!!!